This application claims priority to Japanese Application No. 2000-066960 filed Mar. 10, 2000, incorporated herein by reference.
1. Field of the Invention
This invention is directed to a semiconductor device and a manufacturing method of the semiconductor device. More particularly to a semiconductor device having a gate insulating film structure including an insulating film which contains metal, silicon and oxygen, for example, a metal silicate film and the manufacturing method thereof.
2. Description of the Related Art
It is desirable to make a thin gate insulating film for the miniaturization of the Metal Insulator Semiconductor Field Effect Transistor (xe2x80x9cMISFETxe2x80x9d). If a thin silicon oxide film or silicon oxide-nitride film is used as the gate insulating film, a leak current, that is, a direct tunnel current is increased due to a reduction in the film thickness. As a result, the minimum thickness is approximately 2 nm.
Therefore, it is proposed to suppress a leak current by using a metal oxide film or metal silicon-oxide film (hereinafter referred to as a metal silicate film) having a dielectric constant larger than that of the silicon oxide film. That is, when a metal silicate film or a metal oxide film is used as a gate insulating film, the film thickness for attaining an electrical characteristic equivalent to that of a silicon oxide film (xe2x80x9ceffective film thicknessxe2x80x9d) can be reduced.
However, when the metal oxide film is used as the gate insulating film, it is difficult to obtain a good interface which is free from distortion in a portion facing a silicon substrate. Additionally, when the metal silicate film is used as the gate insulating film, a mediocre interface is attained, with a smaller dielectric constant than that of the metal oxide film.
It was postured to form a metal silicate film at the interface between a silicon substrate and a metal oxide film by heat treatment after formation of the metal oxide film on the silicon substrate so as to form a laminated structure of the two films on the silicon substrate. Unfortunately, with time, the constituent metals of the two films become the same. Therefore, it is difficult to attain the best combination of the metal oxide film and metal silicate film by using different kinds of the constituent metals of the two films. Additionally, since metal oxide film is made of a crystalline metal oxide material, the effective film thickness locally varies due to its dependency on the dielectric constant of the crystal plane orientation.
The metal oxide film and metal silicate film are formed by a Chemical Vapor Deposition (xe2x80x9cCVDxe2x80x9d) method, but a metal oxide film formed by the CVD method has a composition slightly different from a stoichiometric composition and tends to become a coarse film with a low density.
When two MISFETs with different gate insulating film thickness are formed on the same semiconductor substrate, the process of forming a metal oxide film on the entire surface of the substrate, removing part of the metal oxide film on the gate region of one of the MISFETs whose gate insulating film is made thin and forming a metal oxide film on the entire surface of the resultant structure are required. Unfortunately, this process is complicated and inefficient.
Thus, using a metal oxide film or metal silicate film as an insulating film a dielectric constant larger than that of a silicon oxide film is proposed. However, there are many problems in maintaining the characteristics of the gate insulating film while attaining the reduction in the physical and/or the actual film thickness. Specifically, problems with respect to the characteristic of the resulting elements and the productivity of manufacturing the elements.
Accordingly, the object of the present invention is to solve these problems by providing a semiconductor device having a metal oxide film or an insulating film containing metal, silicon and oxygen. Specifically, the present invention provides a metal silicate film as a gate insulating film where the characteristics of the elements in a semiconductor device and the productivity of manufacturing miniature semiconductor device are enhanced and its manufacturing method thereof.
A semiconductor device according to present invention has a gate insulating film including an insulating film with metal, silicon and oxygen, for example, a metal silicate film having at least one of fluorine and nitrogen.
According to the object of the present invention, the dangling bond on the interface between the metal silicate film and silicon that made up the semiconductor substrate can be brought to an end by fluorine contained in the metal silicate film. Therefore, the interface state density can be lowered as compared to a metal silicate film without fluorine and a good interface characteristic is attained.
Further, the dielectric constant of the metal silicate film is increased and the effective film thickness reduced when it contains nitrogen. The annealing process for the metal oxide film is carried out under an oxidizing atmosphere (to compensate for oxygen deficiency) to avert the oxidizing reaction in the interface between the metal silicate film and silicon which made up the semiconductor substrate. Thus, the effective film thickness is reduced and good interfacial characteristic such as a low interface state density is attained.
Thus, a high performance transistor is produced by positioning a metal-containing metal silicate insulating film, having silicon, oxygen, and at least one fluorine and one nitrogen between the semiconductor substrate and the metal oxide film. The transistor thus produced has a good interfacial characteristic with a film gate insulating film containing metal silicate film that has a reduced effective film thickness and a reduced leak current.
A semiconductor device according to another aspect of the present invention has a gate insulating film constructed by laminating a metal silicate insulating film having metal, silicon, and oxygen together with an amorphous metal oxide film. The gate insulating film having the metal oxide film and metal silicate film thus produced has a reduced effective film thickness and a reduced leak current. Further, since the metal oxide film is an amorphous film, a transistor thus produced has a reduced variation of the effective film thickness which depends on the dielectric constant of the crystal plan orientation and a less variation in the threshold voltage with excellent reliability.
Moreover, the metal oxide film in accordance with the present invention is formed after formation of the insulating film with metal, silicon, and oxygen. This is contrary to the industrial practice of forming the metal, silicon and oxygen containing insulating film by heat treatment after the metal oxide film is formed. The metal constituent of the metal oxide film can be replaced from the main metal constituent of the insulating film containing metal, silicon, and oxygen. Further, the insulating film containing metal, silicon, and oxygen and the amorphous film of the metal oxide film can be obtained by changing the heat treatment to a lower temperature than the crystallization temperature of the insulating film containing metal, silicon, and oxygen and higher than the crystallization temperature of the metal oxide film after the formation of the insulating film containing metal, silicon, and oxygen and before the formation of the metal oxide film.
Further, the present invention is a manufacturing method of a semiconductor device having a metal oxide film as one of a multi-layered gate insulating film. The invention is characterized by effecting the heat treatment in an atmosphere containing a plurality of gases with different oxidizing powers after the formation of the metal oxide film on the semiconductor substrate. In other words, the different oxidizing powers can be explained as different tendency for an oxidation-reduction.
Conditions for heat treatment are set to only oxidize the metal contained in the metal oxide film without oxidizing silicon in the boundary region between the semiconductor substrate and the metal oxide film.
In this invention, the insulating film containing metal, silicon, and oxygen is termed xe2x80x9cmetal silicon-oxygen filmxe2x80x9d (metal silicate film). However, the metal silicon-oxygen film can be used when metal oxide and silicon oxide are separated, as a mixture and when metal, silicon, and oxygen uniformly exist as a compound. Any of these uses described for metal silicate film are suitable in the present invention.
In this disclosure, xe2x80x9ccomprisingxe2x80x9d, xe2x80x9ccomprisesxe2x80x9d and the like can have the meaning ascribed to them in U.S. Patent Law and can mean xe2x80x9cincludesxe2x80x9d, xe2x80x9cincludingxe2x80x9d and the like.
These and other embodiments will be described and/or will be obvious from the following detailed description.